Synthesis of Adamantane Derivatives. 50. Facile Synthesis of 2,4-Oxa-Bridged Protoadamantanes and Their Conversions to 2-Substituted and 2,4-Disubstituted Protoadamantanes and a 2,4-Disubstituted Adamantane

Article abstract of DOI:10.1021/jo01307a018

Intramolecular Paterno-Buechi reaction of 3-endo-acylbicyclo<3.3.1>non-6-enes 1a,b proceeded regioselectively to afford exclusively 2,4-oxa-bridged protoadamantanes 2a,b in good yields.The oxetane rings of 2a and 2b were cleaved by addition of hydrogen halides and by reduction with LiAlH4, affording stereospecifically the corresponding 2,4-disubstituted and 2-substituted protoadamantane derivatives 7a, 7b, 9, and 10, respectively.Dehydration of 2-exo-methyl-2-endo-hydroxyprotoadamantane (10) with POCl3-pyridine gave 2-methyleneprotoadamantane (11), while dehydration of the corresponding 4-exo-chloro derivative (7b) afforded exclusively 4(e)-chloro-2-methyleneadamantane (14) as a rearranged product in a high yield.